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  • 1
    Electronic Resource
    Electronic Resource
    Numerical simulation of electromagnetic acoustic transducer in the time domain (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 89-98 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel multistage numerical modeling approach to simulate acoustic-wave generation and propagation of an electromagnetic acoustic transducer (EMAT) is presented. The model assumes a uniform static magnetic field in a conducting half-space. A meander coil winding situated above the half-space is driven by a transient high-frequency current pulse. The numerically computed eddy currents in the conducting specimen are combined with the static magnetic field to yield spatially and temporally diffusive Lorentz forces which in turn are coupled into the elastic-wave equation. This hyperbolic elastodynamic system is solved for the displacement field vector which gives rise to propagating elastic waves. Numerical transduction results are discussed for a generic two-wire transient EMAT configuration and for an isotropic half-space with electric and acoustic material parameters equivalent to those of aluminum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347662
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  • 2
    Electronic Resource
    Electronic Resource
    Isotropic Raman line widths in binary mixtures of van der Waals liquids: A comparison between isotopically and chemically diluted states of liquid methyl iodide (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7463-7476 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: To analyze vibrational depopulation and dephasing mechanisms of polyatomic liquids, the presently most comprehensive study on the dilution behavior of isotropic Raman line widths has been made. By way of example, and following early proposals of Evans and Yarwood [Adv. Mol. Relaxation Int. Processes 21, 1 (1981)], liquid methyl iodide (MeI) was chosen. The low temperature study (T=207 K) covers the detailed concentration dependencies (x) of the isotropic half-widths (FWHH) in total 17 (of 18 possible) polarized fundamentals of CH3I and in the isotopically modified molecules CH2DI, CHD2I, and CD3I (12CD3I) (i) in chemical mixtures with xenon and (partially) CF3I and (ii) in all the six binary isotopic mixtures of the isotopic species above. Furthermore, isotopic and chemical dilutions are combined in ternary mixtures of type (CX3I)0.014−(CY3I)x−0.014−Z1−x with X, Y=H, D and Z=Xe, CF3I, where the trace CX3I has been investigated to study the modulations of the vibrational transition frequency by changes of the intermolecular potential in an isotopically diluted state free of vibrational resonance coupling. The manifold of curves FWHHiso(x) are discussed in terms of a recent Raman line shape theory of Bratos and Tarjus [Phys. Rev. 32A, 2431 (1985)] which explicitly considers the time-dependent cross correlation between the environmentally induced frequency shifts Δωei(t) and those induced by (intermolecular) resonance coupling (RC) ΔωRC(t). Overall, strong indications have been found that intermolecular coupling Δωij=ωi−ωj play a very significant role in line broadening. This holds true not only for the bending modes (as known beforehand), but also for the C–H (C–D) and C–I stretching modes. However, to be effective, these coupling has to be of a strictly resonant nature, i.e., near-resonant transitions with 0.05≤(h-dash-bar)||Δωij||/kBT(very-much-less-than)1 are ineffective in line broadening in the same way as strictly off-resonant transitions with (h-dash-bar)||Δωij||/kBT(approximately-greater-than)1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465728
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  • 3
    Electronic Resource
    Electronic Resource
    Atomic nitrogen ion beam from a pulsed duoplasmatron ion source : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2616-2618 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A duoplasmatron ion source fed with nitrogen usually produces a N+ fraction of approx. 60% in dc mode. In pulsed mode, the duoplasmatron ion source turns out to be a nearly perfect source for atomic nitrogen ions with a high fraction of more than 90% in the milliampere range. This is achieved by pulsing the arc discharge and not by use of any filter magnets. Parameters of operation will be given, such as the comparatively low gas inlet pressure and the arc current, which far exceeds the arc current in dc mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142855
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  • 4
    Electronic Resource
    Electronic Resource
    Metal ion production in ECRIS (invited) : Proceedings of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2795-2800 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The most popular methods of producing ions of solid elements are recalled: (a) utilization of gaseous compounds; (b) oven techniques; (c) insertion techniques, which thanks to the ECRIS plasma confinement enable heating the metallic sample up to unparalleled temperatures (yielding enough vapor even for the most refractory elements); and (d) wall recycling techniques which play an important role in the ECRIS behavior. Typical ion yields for various elements are shown, comparisons are done, and a few practical hints are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142810
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  • 5
    Electronic Resource
    Electronic Resource
    Atomic force microscope with magnetic force modulation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 639-643 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed a scanned stylus atomic force microscope (AFM) with direct force modulation and integrated microfluorescence optics. The instrument was designed to image the surface of massive samples under various ambient conditions. In force modulation microscopy the imaging force is modulated during the scanning process via an external magnetic field that acts directly on the magnetic AFM tip. Polymeric Langmuir–Blodgett films on silicon oxide were imaged to evaluate the application range of the instrument. We demonstrate that direct force modulation microscopy permits the quantitative recording of the local complex compliance both as a function of the location and as a function of the frequency. In a novel imaging mode referred to as sample resonance mode, the contrast of the image can be selectively enhanced based on local elasticity differences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145130
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  • 6
    Electronic Resource
    Electronic Resource
    Status of development of ECR ion sources at Grenoble (invited) : Proceedings of fifth international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1051-1056 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article gives a short summary of the performances of the electron cyclotron resonance ion sources (ECRIS) so far built by the Grenoble laboratory; emphasis is given to the high B field Caprice source, a compact in size source delivering high charge states and high intensities. Both the continuous regime of operation, and the pulsed regime having performances enhanced by the afterglow effect, as well as other noticeable effects, are surveyed. The next part of the article deals with the analysis of the data and our present understanding of the ECRIS behavior. At last the present trends of development of ECRIS are examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145113
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  • 7
    Electronic Resource
    Electronic Resource
    High-Tc three-axis dc SQUID magnetometer for geophysical applications (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3809-3813 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A prototype three-axis magnetometer has been developed, intended for geophysical applications, involving high-transition temperature dc superconducting quantum interference devices (SQUIDs). Each SQUID was fabricated from a thin film of YBa2Cu3O7−x deposited on a SrTiO3 bicrystal to form two Josephson junctions, and was directly coupled to a single-turn pickup loop patterned in the same film. The three orthogonally mounted sensors were immersed in liquid nitrogen in a fiberglass Dewar and operated in separate flux-locked loops. In nominally zero ambient magnetic field, the best magnetic field resolution was 170 fT Hz−1/2 in the white noise, increasing to 225 fT Hz−1/2 at 1 Hz. The dynamic range was ±1.6×106 Hz1/2 in the white noise, and the highest slew rate achieved was 1.6 mT s−1, at 900 Hz. The 3 dB point in the frequency response was about 90 kHz. The three channels were mutually orthogonal to about 1%. The three-axis magnetometer was also operated outside the laboratory in the presence of 60 Hz and radio-frequency noise. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145169
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  • 8
    Electronic Resource
    Electronic Resource
    Quantization error of slit-grid emittance measurement devices : Proceedings of 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1462-1464 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Slit-grid emittance measurement devices usually do not scan the beam continously but in fixed linear (x) and angular (x') steps. Thus in an emittance measurement performed with a slit-grid system, the beam is represented by a number of phase space boxes with a constant area or volume determined by the linear and angular resolution. Considering the emittance as the area in the two-dimensional subspace (x,x') covered by the beam, the quantization error and its dependence on the resolution (linear and angular) as well as the influence of the beam parameters is discussed. Measuring the very low emittance of the high efficiency source (HIEFS) proved that the quantization error can be unacceptably high ((very-much-greater-than)100%). With an optimized measuring device, the normalized emittance came down from 10−1 to 3.6×10−3 π mm mrad. Finally, a typical misleading result of an emittance measurement, caused by the quantization error, is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144946
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  • 9
    Electronic Resource
    Electronic Resource
    Bandwidth enhanced metal-semiconductor-metal photodetectors based on backgated ip structures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2223-2225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on theoretical and experimental results on a novel metal-semiconductor-metal (MSM) photodetector with a backgate provided by a p-doped layer. The backgate allows extremely short sweep-out times for the holes, due to strong electric fields normal to the surface. Thus, long tails due to slow moving holes and screening of the external drift fields by hole space charge accumulation at high optical power, which lead to a degradation of the time response of conventional MSM photodetectors, are avoided. The high frequency performance measured up to 8 GHz in the time and frequency domain showed a significant reduction of the bandwidth limiting hole tail compared to standard MSM photodetectors. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112767
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  • 10
    Electronic Resource
    Electronic Resource
    On the origin of photoluminescence in spark-eroded (porous) silicon (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2771-2773 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence measurements and high-resolution transmission electron microscopy studies on spark-treated (porous) silicon have been performed. Contrary to suggestions put forward by others, it has been found that spark erosion does not yield structures comparable to those obtained for irradiated, that is, damaged silica. Instead, evidence is given that spark treatment of single crystalline silicon wafers produces randomly oriented nanometer-sized silicon crystallites surrounded by a SiO2 matrix. This configuration is believed to be responsible for the observed room temperature visible photoluminescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110792
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